A PHYSICAL MODEL OF CYCLIC CREEP DEFORMATION IN TERMS OF THE EFFECTIVE STRESS

The cyclic creep deformation mechanism of Al + 4.6%Mg alloy at the temperature range of 0.4–0.6Tm is investigated in terms of the effective stress. The peak stress applied for the cyclic creep tests varied from 48 to 180 MPa. It is observed that the effective stress is increasing with increasing applied stress and test temperature. For static creep, the effective stress is constant during the secondary state, on the other hand, for cyclic, it is varying with the alternating stress. For cyclic creep, the peak effective stress is measured to be higher than that of static one under same temperature and applied stress. The activation energies for both static and cyclic creep are observed to be a function of the effective stress. The measured activation energies are in good agreement with the calculated valves from the equation of Qo - V·σe. These experimental observations and analysis strongly suggest that the creep deformation for both static and cyclic is controlled by line defect mechanism or dislocation glide process.